Crystal Initiation Structures in Developing Enamel: Possible Implications for Caries Dissolution of Enamel Crystals

Area of Science:

• Biomineralization
• Materials Science
• Microscopy Techniques

Background:

• Developing enamel crystals exhibit a complex subunit structure.
• Previous studies using Atomic Force Microscopy (AFM) and Chemical Force Microscopy (CFM) on mature enamel suggested substructures of ~10-15 nM.
• Freeze fracturing/etching revealed ~30-50 nM structures in developing enamel.

Purpose of the Study:

• To investigate the presence of smaller ~10-15 nM subunits in developing enamel using high-resolution freeze etching.
• To correlate AFM findings in mature enamel with developing enamel structures.
• To understand the role of these subunits in early enamel formation.

Main Methods:

• High-resolution transmission electron microscopy (TEM) of freeze-etched developing rat enamel.
• High-resolution tapping mode AFM imaging of human mature enamel sections.
• Rapid freezing, fracturing, and ice sublimation of enamel samples.

Main Results:

• Both AFM and freeze etching confirmed the presence of ~30-50 nM structures.
• AFM suggested these larger structures are clusters of ~10-15 nM units, possibly in hexagonal or spiral arrangements.
• High-resolution freeze etching revealed ~10-15 nM subunits in developing enamel, particularly within linear arrays of larger structures.

Conclusions:

• Structures of ~10-15 nM in diameter were detected in developing enamel.
• The formation of linear arrays of these subunits may be linked to the development of mineral initiation sites.
• These findings suggest a role for subunit arrangement in matrix protein processing during enamel biomineralization.